JAVA文字列のいくつかの特殊な応用--数字が文字列になって桁数が0を補うなど

public class StringManager {
	/**
	 *          
	 * @param str
	 * @return
	 */
	public String changeToLetter(String str){
		String result = "";
		String[] arr = new String[]{"A","B","C","D","E","F","G","H","I","J"}; 
		for(int i = 0; i